Caffeine can cause a short, but dramatic increase in your blood pressure, even if you don't have high blood pressure. It's unclear what causes this spike in blood pressure. Caffeine could block a hormone that helps keep your arteries widened. Others think that caffeine causes your adrenal glands to release more adrenaline, which causes your blood pressure to increase.
Some people who regularly drink caffeinated beverages have a higher average blood pressure than do those who drink none. Others who regularly drink caffeinated beverages develop a tolerance to it. As a result, caffeine doesn't have a long-term effect on their blood pressure. It seems that caffeine has a stronger blood pressure increasing effect in people who are older than 70 or who are overweight.
If you have high blood pressure, ask your doctor whether you should limit or stop drinking caffeinated beverages. If you're concerned about caffeine's effect on your blood pressure, try limiting the amount of caffeine you drink to 200 milligrams a day — about the same amount as in two 12-ounce cups of brewed coffee. Keep in mind that the amount of caffeine in coffee and other beverages varies by brand. Also, avoid caffeine right before activities that naturally increase your blood pressure, such as exercise, weightlifting or hard physical labor.
To see if caffeine might be raising your blood pressure, check your blood pressure within 30 to 60 minutes of drinking a cup of coffee or another caffeinated beverage. If your blood pressure increases by five to 10 points, you may be sensitive to the blood pressure raising effects of caffeine. If you plan to cut back on caffeine, do so gradually over several days to a week to avoid withdrawal headaches.